Sensor device for determining the degree of wetting and/or soiling on window panes

ABSTRACT

A sensor device for determining the degree of wetting and/or soiling of a pane in a motor vehicle is provided. The sensor device detects the coating of moisture on the outer side of the pane via an optical beam which is arranged in the area of the pane. The sensor device includes a reflector positioned in the pane, the reflector directing the beam through the pane under conditions of total reflection or reflection at the outer side of the pane and at the reflector. The pane additionally includes a light filter which absorbs a selected wavelength of sunlight. The attenuation is reduced via an optically more absorbent layer of the light filter.

RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.09/053,574, filed Apr. 2, 1998 now U.S. Pat. No. 6,052,196.

FIELD OF THE INVENTION

The present invention relates to a sensor device for determining thedegree of wetting and/or soiling on window panes.

BACKGROUND INFORMATION

In motor vehicles, to measure the degree of wetting (i.e., moisture)present in the wiper field of windshields or rear windows, a rain sensoris installed on the inner side of the window. If the wiping system isswitched on in the automatic operating mode, and the window is wettedwith moisture at the location where the sensor is installed, a wipingoperation is initiated.

The mode of operation of the sensor is based on an optical principle. Inparticular, a light beam of known intensity emitted by a transmitter isintroduced into the pane at a certain location and is directed through adefined length of the pane by means of repeated total reflection withinthe pane. At a second selected location, the light beam is directed bymeans of optical coupling out to a receiver and to a measuring systemwhere the residual light intensity is measured and analyzed.

When the surface of the pane is wetted with drops of water, part of thelight beam is no longer completely reflected, but rather emerges fromthe pane. The resultant loss of intensity of the residual light is ameasure of the pane surface wetting. Below a preselected thresholdvalue, a means for cleaning the window pane is then automaticallyactivated.

Rain sensors of this type are often installed in motor vehicles at thelevel of the rearview mirror to ensure that the driver's vision is notimpaired by the sensor housing. In some motor vehicles, however, a lightfilter, e.g., a green or gray wedge tinting the upper edge of the pane,is situated at this location and is integrated in the windshield. Whenthe wave length of the transmitter beam being used is within a rangethat is essentially attenuated by the light filter, it is not possibleto position the optical rain sensor in the light filter, since therepeated total reflection in the pane causes the light beam to passthrough the light filter several times, attenuating it to anunacceptable degree.

SUMMARY OF THE INVENTION

The sensor device of the present invention has the advantage that thetransmitter beam of the rain sensor, in passing through the pane, istotally reflected or reflected at a reflecting means in the pane, suchthat the attenuation resulting from the optically more highly absorbentlayer of the light filter is reduced.

Since the conventional windshield of an motor vehicle is comprised of acomposite of a plurality of layers, and the light filter is normallydesigned as an optically more highly absorbent layer of the laminatedglass, a reflecting means can be mounted between this layer and theexternal layer which faces away from the interior of the motor vehicle,so that the transmitter beam is directed through the pane, underconditions of total reflection or reflection at the outer side of theouter layer and at the reflecting means.

Another advantage of the present invention is that the reflecting meanscan be realized in various ways, so that for laminated glass panes thatare variously manufactured or executed, optimal solutions can be found.

Yet another advantage of the present invention is that the optical pathsof the light beam in the pane are shorter, the paths being generated bythe reflecting means. Thus, assuming a constant length of the measuringdistance of the rain sensor, the result is a larger number ofreflections, so that an even (homogeneous) illumination of the measuringdistance is provided. In this way, the sensitivity of the rain sensor inthe area of the measuring distance is evened out (homogenized) and thusincreased.

A further advantage of the present invention results from thepossibility of eliminating the heating device for heating the inner sideof the pane, since the wetting of the inner side of the pane, e.g.,through condensation water, exerts practically no additional influenceon the moisture-dependent weakening of the signal and thus on thefunctional reliability of the rain sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross section of a sensor device, comprising an opticalrain sensor situated on a conventional pane.

FIG. 2 shows a cross section of a pane in the area of the measuringdistance of the rain sensor, according to a first exemplary embodimentof the present invention.

FIG. 3 shows a cross section of an improved pane in the area of themeasuring distance of the rain sensor, according to a second exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an optical rain sensor mounted on a glass pane 10. Pane 10may be, for example, a rear window or another pane whose wetting is tobe measured. The rain sensor includes as a transmitter 12, e.g., a diode(LED), and a receiver 14, e.g., a photo diode. The transmitter 12,receiver 14, together with two photo conductors 16′, 16″ and a part ofpane 10, constitute an optical measuring circuit. Light emerging fromtransmitter 12 is focussed at an entry lens 15 of first photo conductor16′ and is deflected towards total-reflecting surfaces, so that, at anoutput face, it can penetrate into windshield pane 10 at a selectedangle as a nearly parallel light beam 18.

With conventional panes 10, after light beam 18 penetrates into pane 10,the beam 18, at outer side 32 and at inner side 30 of pane 10, istotally reflected and/or reflected several times.

At a suitable location, light beam 18 reaches receiver 14, via secondphoto conductor 16″ having a lens-like, curved light-conducting outputface 19 and an aperture 20. The quantity of light received by receiver14 changes as a function of the degree of wetting of pane 10, since, asa result of rain drops 21 situated in the measuring range of the rainsensor, part of light beam 18 passes through pane 10. The signal ofreceiver 14 is subsequently conducted to an evaluating electronics 22situated within or outside the rain sensor, where it is processed andevaluated.

The rain sensor and parts of evaluating electronics 22 are arranged in ahousing 23. This housing 23, for example, is clipped onto metal clampingconnections, which are glued to pane 10.

FIG. 2 shows a cross section of a pane 10 in the area of the measuringdistance of the rain sensor in accordance with the present invention.Pane 10 is a laminated glass pane having an inner pane 24 facing themotor vehicle interior, an outer pane 26, and, as a light filter, atinted (or dyed) laminated glass film 28 arranged between the otherlayers, which absorbs light of a selected wave length more than inner orouter panes 24, 26. The light filter attenuates the sunlight of aselected wave length range, so that the driver of the motor vehicle isnot blinded. In accordance with the invention, a reflecting means 34 isarranged in the area of the measuring distance between inner side 36 ofouter pane 26 and film 28, which is more absorbent.

The sensor device of the present invention shown in FIG. 2 functions asfollows. In accordance with the present invention, a reflecting means 34is arranged in the area of the measuring distance of the rain sensorsuch that the attenuation of light beam 18 by film 28 is reduced, inthat light beam 18 traverses film 28 only during the injecting andcoupling-out of light beam 18 in or out of pane 10, respectively.Between the injecting and coupling-out of light beam 18, light beam 18,which is evaluated in evaluating electronics 22, is reflected, at thesurface of reflecting means 34, back to outer side 32 of pane 10 anddoes not reach film 28, which is more absorbent.

Reflecting means 34, for example, can be arranged on inner side 36 ofouter pane 26 or on the surface of film 28. It is equally possible toinsert reflecting means 34 between outer pane 26 and film 28.

For reflecting means 34, for example, a thin metal film, preferably madeof aluminum, or a metallically vapor-deposited thin plastic film may beemployed. It can be arranged, with adhesive bonding, on inner side 36 ofouter pane 32. This reflecting means 34 is nevertheless visible.

A further specific embodiment of reflecting means 34 can be realized byan essentially transparent film or layer (coating), whose refractiveindex is different from that of pane 10. The difference in refractiveindex causes, at reflecting means 34, a reflection of part of diagonallight beam 18. If reflecting means 34 is selected optimally, the lighttransmission of pane 10 will, in this case, be improved for light beam18 emitted by transmitter 12, and/or the losses that are independent ofwetting will be reduced.

Reflecting means 34 can also be realized through directly coating innerside 36 of outer pane 32, e.g., through brushing on, vapor depositing,or adhesion bonding.

Reflecting means 34 is generally adjusted to the light emitted from thetransmitter 12 and having a known wave length, such that reflectingmeans 34 reflects the light of this wave length the most (in comparisonwith other wave lengths).

Due to the shorter optical paths of light beam 18 in pane 10, given aconstant length of the measuring distance, the number of totalreflections or reflections increases, resulting in a more evenillumination of the measuring distance, i.e., of outer side 32 of pane10. In this way, the sensitivity of the rain sensor is evened out in thearea of the entire measuring distance.

If reflecting means 34 is used, neither condensation water nor any othertype of wetting on inner side 30 of inner pane 24, both of which areundesirable with conventional sensor devices, has any further influenceon the functional reliability of the rain sensor, since no totalreflection takes place on the inner side 30 of pane 10, which would thuscause a possible coupling-out of light beam 18 during wetting.Therefore, condensation water on inner side 30 cannot lead to aweakening of the signal at receiver 14. As a result, there is no needfor heating in the rain sensor, intended to prevent condensation oninner side 30 of inner pane 24.

FIG. 3 shows a further exemplary embodiment of the sensor device of thepresent invention in a cross section of pane 10 in the area of themeasuring distance of the rain sensor, analogously to FIG. 2. Pane 10includes a composite of layers, having an inner pane 24, an outer pane26, and a film 28 inserted between two panes 24, 26, the film 28 beingpunched out at inner side 36 of outer pane 26, in the area of an innertotal reflection of light beam 18.

The punching out takes place during the manufacture of pane 10. Insubsequently assembling two panes 24, 26, a hollow space is formed as areflecting means 34 for light beam 18, the hollow space, depending onthe manufacturing process, being filled with humidity-free air at lowpressure, or containing a vacuum.

As a result of the relationship of the refractive index of outer pane 26and the air or vacuum in the hollow space, as well as of the refractiveindex of the angle of incidence of light beam 18, the latter movesthrough a total reflection, at inner side 36 of outer pane 26, and atouter side 32 of outer pane 26. In the hollow space, however, nohumidity can accumulate which might result in parts of light beam 18being coupled out from outer pane 26 and passing into the hollow spaceand inner pane 24. Therefore, the total reflection in pane 10 isindependent of humidity.

What is claimed is:
 1. A pane for a motor vehicle, comprising: aplurality of layers; and a reflector arranged between two of theplurality of layers for reflecting a light beam, the reflector beingarranged to direct the light beam at an outer side of the pane and atthe reflector under a condition of at least one of total reflection andreflections; wherein, within a portion of the pane that is coextensivewith a length of the reflector, the beam is reflectable within the panein a path bounded by the outer side of the pane and a side of thereflector facing the outer side of the pane.
 2. The pane according toclaim 1, wherein the plurality of layers include a first layer and anouter pane layer the first layer being optically more absorbent than theouter pane layer, the reflector being positioned between the first layerand the outer pane layer.
 3. The pane according to claim 2, wherein thefirst layer includes a light filter, the light filter including one of atinted laminate glass film and a poly vinyl butyryl.
 4. The paneaccording to claim 2, wherein the reflector is one of i) mounted on aninner side of the outer pane layer, ii) mounted on a surface of thefirst layer, and iii) inserted between the outer pane layer and thefirst layer.
 5. The pane according to claim 1, wherein the reflectorincludes at least one of a metal film and a metallically vapor-depositedplastic film.
 6. The pane according to claim 1, wherein the reflectorhas a refractive index that is different from a refractive index of anadjacent one of the plurality of layers.
 7. The pane according to claim1, wherein the reflector is one of i) coated on an adjacent one of theplurality of layers, ii) vapor deposited on the adjacent one of theplurality of layers, and iii) adhesively bonded to the adjacent one ofthe plurality of layers.
 8. The pane according to claim 1, wherein thereflector includes a hollow layer, the hollow layer being filled with agas and having a refractive index that is different than a refractiveindex of an adjacent one of the plurality of layers.
 9. The paneaccording to claim 1, wherein the reflector includes a hollow layerhaving a vacuum and having a refractive index that is different than arefractive index of an adjacent one of the plurality of layers.
 10. Thepane according to claim 1, wherein the beam is reflectable within theportion of the pane that is coextensive with the length of the reflectora number of times that is greater than another number of times the beamis reflected in another portion of the pane that is outside the portionof the pane that is coextensive with the length of the reflector. 11.The pane according to claim 2, wherein the beam does not impinge on thefirst layer when the beam travels through the portion of the pane thatis coextensive with the length of the reflector.